1. The Field of the Invention
The invention is in the field of apparatus and methods for forming soilcrete columns and walls and grids in situ in soil.
2. The Related Technology
For a number of years, multi-shaft auger machines have been used in Japan to construct concrete-like columns in the ground without having to excavate the soil. These columns are sometimes referred to as "soilcrete" columns. Soilcrete is a term applied to a mixture of soil and a chemical hardener, which sets up as a solid mass, much like concrete. The chemical hardener is injected directly into the soil in situ, and mixed with the soil, by means of an auger, thus avoiding the necessity of removing the soil and replacing it with concrete as is necessary when constructing concrete columns or walls in the soil.
In many cases the soilcrete columns have been overlapped to form boundary walls or structured retaining walls. In other cases the soilcrete columns have been overlapped in orthogonal directions, thus forming a grid. This latter application is particularly useful in situations wherein the soil is contaminated, such as with toxic wastes. The resultant grid solidifies as a solid mass, substantially impervious to migration of the contaminants as a result of ground water flow.
The related technology discloses apparatus and methods for forming, in situ, adjoining soilcrete columns in soil wherein two or more overlapping boreholes are simultaneously formed by joined and cooperating augers actuated by a drilling rig, wherein adjacent augers are both horizontally and vertically offset from each other, and positioned with respect to each other such that the augers avoid interfering with each other while still allowing the resultant boreholes to overlap. Normally the boreholes are augered down to bedrock, and usually slightly into the bedrock so as to key into it. However, since adjacent augers are necessarily vertically offset in order to avoid interference with each other while still forming overlapping boreholes, one or more augers will reach bedrock before the adjacent one or ones do so. It then becomes necessary to drill the first auger(s) substantially into the bedrock until the adjacent auger(s) reach the bedrock. This is a time-consuming, costly, and functionally unnecessary operation which it would be desirable to avoid if possible.
In most applications it is preferred that the columns be formed so as to be overlapping with no, or at least a minimum, of interstitial spaces therebetween. This leads to the problem as noted above wherein adjacent augers do not reach bedrock at the same time. Thus the problem to be solved in order to improve over the prior art is to conceive apparatus and methods which will permit the augers to reach bedrock substantially simultaneously and yet will permit the soilcrete columns to overlap.